Variable denier yarn apparatus



June 6, 1967 J. w. MOTTERN ETAL 3,3

VARIABLE DENIER YARN APPARATUS Original Filed Oct. 14, 1963 INVENTORS JON W.{i//7OTTERN ATTORNEY United States Patent 3,323,165 VARIABLE DENIER YARN APPARATUS John W. Mottern, Cary, and Bruce van Voorhis, Raleigh, N. (3., assignors to Monsanto Company, a corporation of Delaware Original application Oct. 14, 1963, Ser. No. 316,027. Di-

vided and this application Apr. 20, 1966, Ser. No. 543,876

3 Claims. (Cl. 18-1) This application constitutes a divisional of our copending application Serial No. 316,027, filed Oct. 14, 1963.

This invention relates to an apparatus for producing thick-thin yarns from synthetic thermoplastic material. More particularly, it relates to an improved apparatus for producing thick-thin yarns from thermoplastic continuous filaments by selective drawing or elongation. It will be understood that, where the context permits, the term yarn denotes both monoand multi-filament tows or yarns.

It is well known, in the utilization in synthetic organic polymers for the preparation of filamentary structures, to introduce non-uniformities of diameter or denier at intervals along their lengths. Products prepared in this way can be made into fabrics for textile and other end-uses having a pleasing hand and attractive surface variations. Also, a fabric constructed of such yarns may be caused to exhibit a pleasing color variegation due to the fact that the undrawn, thick segments possess different dyeing characteristics relative to the drawn, thin segments, the thick segments normally being the deeper dyeing. By virtue of this phenomenon, it is possible to produce colorvariegated fabrics by the single application of one dye, a proposition of obvious economic advantage. Also, such fibers or filaments may be caused to simulate natural fibers which are known to have a slub content, such as, for example, linen and dupioni silk.

One process by which such thick-thin or nubby yarns have been made is to introduce variations in the feed rate at which the polymeric material is supplied during the spinning operation. The variations can be regular or random in nature and, for many purposes, it is desirable that they be random. A great deal of ingenuity is displayed by the prior art in the employment of various mechanical or electronic devices productive of a true random or non-uniform distribution of feed variations. Frequently, such variations are introduced by altering the speed of operation of a positive displacement spinning pump.

Another way of producing thick-thin filaments is by varying the rate of draw-down of the filaments in the course of their production from the spinning jet through which they are extruded. This can be done by drawing the filaments along a path whose length is caused to vary periodically or randomly, the filaments being passed over a deflecting surface, e.g. a cam, cam-operated guide or the like, which moves transversely of the filament path so as to deflect the filaments from their normal shortest route. The filaments are drawn away from the spinning jet at a higher linear rate while the path is lengthening, to thereby produce thin segments in the filaments, and at a lower rate while the path is shortening so as to produce relatively thick or undrawn segments or slubs in the filaments. It has been found that in order to produce definite and pronounced thick segments of reasonably sharp demarcation between the thin segments, it is desirable that the movement of the deflecting surface to a position corresponding to the shortened path of the filament be as sudden and abrupt as possible. However, the

speed with which the deflecting surface can be moved for this purpose is limited by considerations of inertia of the filaments and mechanical limitations inherent in the apparatus for the purpose.

Still another way in which non-uniformities in yarn diameter have been obtained is by taking advantage of a characteristic of synthetic or organic polymers known as cold-drawability. Synthetic fibers in general are improved in strength, durability, and dimensional stability by orienting the molecules or crystal-like substructures which constitute the filament by subjecting the filament to a cold-drawing procedure, that is, by elongating the filament after its formation in an irreversible manner, generally to approximately 2 to 6 times its original length. Under some circumstances, particularly in cases where the filament can be plasticized or softened by heat, an increase in length of 20 or more times its original length can be obtained without molecular or crystallographic orientation. Naturally, since the amount of material present in the fiber is constant, when a fiber is increased in length it necessarily experiences a decrease in its diameter.

If the drawing process is applied to a fiber in a sporadic or non-uniform fashion, variation in yarn diameter will be achieved due to the fact that not all of the full length of the fiber will be drawn the same amount. Thus, it is possible to obtain fibers of non-uniform diameter in 'which the sections of great diameter are substantially undrawn and nnoriented, or at most partially drawn and partially oriented. There are, in addition, other ways by which it is possible to introduce variation in diameter of fibers produced from synthetic organic polymers. For example, it is known to include, at intervals along the length of a filament, quantities of an inert material, such as sand or the like, which will not decrease in diameter during the drawing process, but this results in a weakening of the filament structure so that breakage of the filament at the point of increased diameter is apt to occur. Another method is to apply to a uniform filament a non-uniform surface coating of some adherent material, but this approach suffers from the tendency of such non-uniform coatings to snag, if they are permanent, while, other-.

wise, they are apt to rub off during processing.

In the production of thick-thin yarns, the need is. therefore apparent for an improved and simplified apparatus which operates in a manner to avoid the above related difiiculties.

It is, therefore, an object of the present invention to provide an improved apparatus for producing thick-thin filamentary structures.

A further object of this invention is the production of thick-thin filamentary structures by subjecting such structures to selective elongations.

A further object of this invention is an improved apparatus for producing thick-thin filamentary structures by means of intermittent application of radiant heat to such structures while maintained under uniform drawing tension.

Another object of our invention is an improved appara tus for use in producing thick-thin filamentary structures, which apparatus is designed to accomplish intermittent radiant heating of such structures while they are subjected to a draw ratio below their natural draw ratio.

In accordance with our invention, the above and still other objects are achieved by providing an apparatus for producing variable denier filamentary structures, which apparatus comprises means to propel the yarn under a uniform drawing tension and means to effect a simultaneous, intermittent application of radiant heat to the yarn. In a specific embodiment, the application of radiant heat is accomplished by a solenoid-actuated incandescent coil which is reciprocated in and out of close proximity a to the yarn path to thereby effect selective, intermittent drawing of the yarn being processed.

The invention will be more clearly understood by reference to the following detailed description and accompanying drawing, which shows a simplified embodiment of one form of the apparatus which may be employed in the practice thereof.

As previously mentioned, our invention contemplates the intermittent application of radiant heat energy to a yarn being drawn to a ratio less than its natural draw ratio. By the phrase natural draw ratio is meant a draw ratio at which a certain degree of permanent, non-reversible extension is imparted to the polymeric material which is just sufficient to change it from its undrawn state to a uniformly drawn and highly oriented state without straining the polymeric material to the point of introducing surface cracks or failure. In general, when any material is drawn in the conventional sense used in processing synthetic fibers, one or both of two phenomenon will normally be observed; there can be plastic flow and there can be orientation of the material. The plastic flow mode of drawing is used to elongate a polymeric material 10 to more than 100 times its original length. However, in the plastic flow process, only slight orientation of the material occurs. Plastic flow drawing is normally carried out under conditions of either high temperature or moisture, or in the presence of other plasticizing agents, or both. There is no natural draw ratio, in the sense here employed, for plastic flow elongation. When a synthetic, thermoplastic polymer is not in a plastic condition, it will, under normal conditions, tend to draw at its natural draw ratio and, in the process, become highly oriented. If, for example, an undrawn filament can be drawn to times its original length to produce a highly oriented, uniformly drawn material, it is not possible, in general, to draw it completely at either 4 to 6 times its original length under the same conditions. If one attempts to draw to 6 times the original length, the filament will break; if one chooses a lower ratio of, for example, 4

times, one will find that some sections of the yarn will draw at the natural draw ratio while other sections will not draw at all or only partially.

The natural draw ratio of most thermoplastic filaments is primarily controlled by the yarn temperature immediately prior to the point of draw (hereafter referred to as the drawing temperature), moisture (both that of the material being drawn and that of the ambient atmosphere attending the drawing operation), the as-spun birefringence and the drawing speed. At given conditions of moisture and drawing temperature, there will be a corresponding natural draw ratio for a given specimen at which it will preferentially elongate to the highly oriented, uniformly drawn state. Therefore, when the drawing temperature is selected for given moisture conditions, the natural draw ratio is primarily determined by these conditions for a given specimen. Alternatively it is possible to select a draw ratio, drawing speed and to control the temperature gradient through which the material passes during the drawing step to effect a natural, uniform drawing operation.

The natural draw ratio is also effected by the drawing speed. As the drawing speed is increased and the yarn is held at given conditions of temperature and moisture, the natural draw ratio will normally be found to increase, i.e. to obtain uniform drawing at such conditions, the draw ratio must be increased.

Moisture content of either or both the material being drawn and the ambient conditions attending the drawing is still another parameter affecting the natural draw ratio. In general, for many materials, as the moisture content of the material and/ or ambient atmosphere is increased, there will be reached a point above which uniform drawing will be observed to take place. Conversely for certain thermoplastic polymeric materials, the moisture conditions may be reduced to a point below which drawing, even of the non-uniform variety, is impossible, nylon being one example. As-spun birefringence has been recognized as still another parameter affecting natural draw ratio.

In summary, then, it is recognized that the natural draw ratio for a given thermoplastic, filamentary material is primarily a function of moisture content of the material, relative humidity of the ambient atmosphere attending the drawing operation, the as-spun birefringence of the filamentary structure, the temperature of the material at the point of draw, the draw ratio and the drawing speed. The complementary manipulation of these parameters is largely a matter of art involving trial and error by observation, it being possible to obtain natural drawing, as above defined, under innumerable combinations of these various parameters. It is to be understood that the quantitative aspects of the various factors, already referred to, recognized as effecting the drawing behavior of a molecularly orientatable structure are not considered part of the present invention, nor is a precise understanding of the interplay, quantitatively, of such factors essential to its practice. It need only be recognized that the phenomenon of natural draw, as above defined, does exist and that it is primarily a function of previously enumerated factors which are susceptible to manipulg tion on a trial and error basis to intermittently obtain the conditions requisite to natural, uniform drawing.

In its broadest terms, the essence of the present invention contemplates the concept of drawing a given yarn specimen at a draw ratio less than its natural draw ratio under the prevailing conditions of moisture, as-spun birefringence, draw speed, etc., while equalling or exeeding at timed intervals, of predetermined and variable occurrence and duration, the minimum conditions requisite to natural, uniform drawing, specifically by the time-controlled application of radiant heat energy to thereby elevate chosen segments of the yarn to a temperature exceeding that necessary to effect uniform drawing, i.e., equalling or exceeding the conditions which, in concert with the prevailing, possibly controlled, conditions affecting draw, result in natural, uniform drawing of the particular yarn being processed.

As a practical matter, the only essential to an understanding and practice of the present invention is the recognition of the necessity of subjecting the yarn to a draw ratio which, under the given conditions, is less than the natural draw ratio while intermittently varying one of the conditions effecting natural draw ratio, preferably yarn temperature at the point of draw, to effect natural drawing of spaced segments of the yarn. When the temperature is below that necessary to effect natural, uniform drawing, the draw ratio should be such as will effect, under the prevailing conditions, random or nonuniform drawing, which is uncontrolled and to be avoided. By introducing periodic applications of heat to raise the yarn temperature at the point of draw, such random, uncontrolled drawing is prevented by virtue of the fact that any drawing which takes place is highly preferential to the point or zone of heat application.

There presently exists no practicable means of effecting such periodic applications of heat to the yarn to effect selective drawing. The present invention contemplates the periodic application of radiant heat energy to the yarn, which concept particularly recommends itself to high speed operations in view of its inherent ability to be controlled virtually instantaneously.

The drawing illustrates one possible embodiment of the apparatus utilized to carry out the present invention. Such an apparatus, in simplified form, would include a supply of continuous filamentary thermoplastic material in the form of a supply package or bobbin -10, which material may or may not have been previously processed on a draw-twister. The loose end of the yarn, which may be in the form of either a continuous monoor multi-filament, is passed from the package through a take-off guide 12, the threadline then being strung behind snubbing roll 14 and over feed roll 16. Conventionally, the snubbing roll 14 is spring-biased against the feed roll 16 to maintain a non-slipping uniform feed rate of the yarn to the draw roll 18. After passing the thread line about draw roll 18 and separator roll 20 a sufficient number of turns to prevent slippage, the yarn is passed to a conventional grooved traverse roll 22 which traverses the yarn over take up bobbin 24 to build a package of the desired configuration. The structure described up to this point is a single stage draw arrangement of conventional components, the various driven rolls and take-up mechanism normally being provided with variable speed drives to effect varying draw ratios and draw speeds.

Intermediate the feed roll 16 and the draw roll 18, there is disposed adjacent the thread line a linear actuator 26 which preferably takes the form of a high response, magnetically biased solenoid which is capable of reciprocating at a high rate of speed. The linear actuator is driven by square-wave signal generator 28 of conventional construction, the output amplitude and frequency of which may be controlled over a wide range.

A source of radiant heat energy is mounted by the plunger of linear actuator 26 to be rapidly reciprocated in and out of close proximity to the threadline. Such a radiant heat source preferably takes the form of an incandescent coil 30, a nichrome wire heater being used to good advantage. The linear actuator is so positioned that during the maximum extension of its plunger, the radiant heater 30 is carried to a point just short of touching the threadline. The power output required of the radiant heat source will of course vary with the mass perunitlength of the material being processed, the drawing speed and the slub pattern desired, whether long or short in its variations. One means of controlling the power output is by varying the physical dimensions and mass of the heat source, in this case, the incandescent coil. Another expedient means of controlling the amount of heat transmitted to the threadline may be accomplished by connecting the power lead wire 32 through a variable voltage control which may take the form of a variable transformer 34.

It is apparent from the above description of one embodiment of a novel apparatus for use in practicing our invention that such apparatus is susceptible to ready incorporation into existing commercial equipment with a minimum of modification. For example, where it is desired to process a variable denier yarn on a conventional draw-winder, the only change necessary is the addition of the solenoid-actuated heater coil at a point intermediate the feed and draw rolls. By virtue of the small dimensions of the solenoid-coil, it may readily be accommodated by a draw-winder simply by the addition of a suitable mounting bracket, the heater power source and the signal generator being located in a remote position, if desired.

It has been found that, where nylon is being processed, it is most expedient to control the relative humidity attending the drawing operation at levels below 30% in order to obtain the desired non-uniform drawing while heat is not being applied; otherwise, at higher levels of relative humidity nylon will have a tendency to draw uniformly at room temperature, an occurrence destructive of the operability of the present process. Polyesters, in general, are not so sensitive as nylon to relative humidity and it has been ascertained that the present process may, in many cases, be carried out at normal room conditions. Again, the case of nylon, the critically of the ambient relative humidity may be somewhat minimized by reducing the moisture content of the finish, which may optionally be supplied prior to the selective drawing operation.

The procedure followed in the practice of the present invention is essentially that used during a standard drawing operation with the snub or draw pin omitted. As shown in the drawing, the radiant heater 30, in the form of an incandescent coil, is mounted, with its associated linear actuator, between the feed and draw rolls. A trial frequency is set up on the signal generator (aided by monitoring the generator by an oscilloscope), the linear actuator is energized and the feed and draw drives are activated. The position of the heater on the extension stroke should be adjusted so that it stops just short of contact between the yarn and the heater coil. Preliminary evaluation of the product is easily made by a visual examination of a dyed length of yarn, whereby slub frequency and length are easily measured. Absence of thick portions indicates natural, uniform drawing is taking place and the conditions must be adjusted in the fashion above related to accommodate non-uniform cold drawing. Where it is observed that drawing even of the nonuniform variety is not occurring, it will be necessary to adjust the drawing conditions in an opposite sense to a state productive of non-uniform cold drawing. As previously discussed, this is most easily accomplished by increasing the ambient relative humidity to a value just below the moisture level necessary for uniform drawing. T he invention will be further characterized, but is not intended to be limited by, the following examples.

EXAMPLE 1 A sample of nylon 66 yarn having 34 filaments and an as-spun denier of 310 was drawn at a ratio of 3:1 and a draw speed of 300 yards per minute without employing a draw pin. The radiant heat source was in the form of an incandescent coil constructed of nichrome wire of 20 guage thickness having an overall size of 1% inches long by At-inch wide, operated at a power of 112 watts at 7.5 volts. The yarn was heated by placing the heater as close to the yarn as possible without touching it. The power to the heater was adjusted unitil uniform drawing was obtained which, in this case, was realized at a relative humidity of 30 percent at a power of 112 watts at 7.5 volts. When ambient relative humidity was maintained below the 30% level, it was observed that an undrawn section of yarn was produced if the heater was rapidly retracted from the threadline a distance of at least one-quarter inch. The distinctness of the thick segments depended on how fast the heater was reciprocated from its retracted to its extended position. The heater was reciprooated at a ratio of 23 cycles per second in such a fashion that it dwelled in its extended position for 29 milliseconds and in its retracted position for 14 milliseconds, both values including the time required to travel to and from the retracted position. Thick segments of 1 inch length occurring at a frequency of 4 segments per yard were obtained.

EXAMPLE 2 The same procedure as outlined in Example 1 was followed except that the relative humidity was maintained at 50 percent. Under these conditions, the yarn was uniformly cold drawn without employing a draw pin so that no thick-thin yarn could be produced by intermittent heating.

EXAMPLE 3 The same procedure as outlined in Example 1 was followed except yarn having an as-spun denier of 180 was drawn at a 2:1 ratio. At 30 percent relative humidity, the yarn was uniformly cold drawn. When the humidity was lowered to 21 percent, thick-thin yarn was produced as in Example 1, except that the denier of the thick sections was 150 and that of the drawn sections was 90.

EXAMPLE 4 A sample of polyethylene terephthalate yarn having 30 filament-s with a total undrawn denier of 300 was drawn without employing a snub pin at a draw ratio of 3.65 and at a draw speed of 115 feet per minute. A nichrome wire heater consuming 104 Watts at 7.5 volts similar to that employed in Example 1 was used. The heater was reciprocated at 1.33 cycles per second to produce a thick-thin yarn which was collected on a bobbin and knit-ted into a fabric. The fabric exhibited the expected novel effect, giving a quite pleasing appearance.

EXAMPLE The procedure as outlined in Example 4 was followed except a polypropylene yarn having 4 filaments and a spun denier of about 450 was employed. The yarn was drawn at a ratio of 4:1 without employing a draw pin. Power to the heater, the same used in Example 4, was 90 watts. The heater was reciprocated at a frequency of 2.33 cycles per second. Thick-thin yarn was produced with the thick sections very distinct, due to the large difference in denier of drawn and undrawn sections.

In addition to preparing thick-thin yarns from the materials described in the foregoing examples, this invention may be advantageously employed to prepare such yarns from a variety of other fiber-forming materials, insofar as they are capable of being cold drawn non-uniformly. Such materials may include both natural and synthetic polymers which are capable of being uniformly drawn when suificiently heated under tension at suitable conditions of temperature and moisture. Although yarns which have not been drawn are preferred, partially drawn yarns which may be further drawn upon heating may as well be processed. Yarns prepared from polyamides, polysulfonamides, polyesters, polyurethanes, polyureas, polyacrylonitrile, polyhydrocarbons, e.g., polyethylene, polypropylene, polyvinylchloride, cellulose esters, cellulose ether-s, as well as many others, may be drawn employing the process and apparatus of the present invention.

It may now be appreciated that there has been herewith disclosed a novel apparatus for producing thick-thin yarns, which apparatus makes it possible to exercise a precise control over the slub pattern and which is capable of high reproducibility, making it possible to merge two or more different runs. The application of radiant heat at controlled intervals of predetermined occurrence and duration to a continuously running length of yarn being processed under conditions otherwise productive of non-uniform cold drawing, i.e. below its natural draw ratio, in the absence of the draw pin has been found to fill these objectives in both a simplified and economic manner.

Obviously, numerous modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

What is claimed is:

1. An apparatus for producing yarns exhibiting a variation in denier along their lengths, said apparatus comprising mean-s to propel a running length of yarn under substantially uniform tension, a radiant heat source and means to actuate said radiant heat source in and out of close proximity to said yarn at intervals of predetermined References Cited UNITED STATES PATENTS 2,746,034 5/1956 Kreidl l8l 2,953,427 9/1960 Egger 188 XR 2,975,474 3/1961 Smith 264-288 XR 3,081,485 3/1963 Steigerwald 18-l XR WILLIAM J. STEPHENSON, Primary Examiner. 

1. AN APPARATUS FOR PRODUCING YARNS EXHIBITING A VARIATION IN DENIER ALONG THEIR LENGTHS, SAID APPARATUS COMPRISING MEANS TO PROPEL A RUNNING LENGTH OF YARN UNDER SUBSTANTIALLY UNIFORM TENSION, A RADIANT HEAT SOURCE AND MEANS TO ACTUATE SAID RADIANT HEAT SOURCE IN AND OUT OF CLOSE PROXIMITY TO SAID YARN AT INTERVALS OF PREDETERMINED OCCURRENCE AND DURATION. OCCURENCE AND DURATION. 